Light emitting diodes (LEDs) are used as light sources in many automotive lamp applications. LEDs are fast replacing traditional incandescent light bulbs since they are more energy efficient, have a longer service life and permit shallower packaging compared to most bulb-type assemblies.
Unlike an incandescent filament, an LED is an inherently directional light source meaning that the relative luminous intensity of an LED varies with viewing angle (or direction). The luminous intensity is highest at 0° (normal viewing angle) and drops off significantly as the viewing angle approaches 90°. The effect of this directionality is that an LED appears brightest when viewed directly and becomes dimmer as the viewing angle increases. LEDs used in automotive lamp applications have the drawback that when active, the LEDs appear as a series of discrete “bright” or “hot” spots. The lamp will also be quite directional such that when viewed from an acute angle, the lamp will appear dimmer.
From an aesthetic viewpoint, for an automotive lamp having a series of LED light sources, it would be advantageous to provide a light output of substantially uniform luminance across the viewing surface of the lamp when viewed from more than one direction.
In the past, directional light from LEDs has been diffused by an optical diffuser. An optical diffuser is typically some kind of translucent object that scatters light in all directions. Most diffusers however are inefficient as some light is lost to reflection and not all light passes through the diffuser. This solution, while assisting to spread the directional light to create a uniform appearance, suffers from optical inefficiencies caused by the diffusing medium. In the automotive lighting industry, optical efficiency is an important design driver as manufacturers seek to reduce cost and package size of the lamp.
An object of the present invention is to ameliorate one or more of the above described difficulties or at least provide a useful alternative to arrangements of the type discussed above.
Other advantages of the present invention will become apparent from the following description, taken in connection with the accompanying drawings, wherein, by way of illustration and example, a preferred embodiment of the present invention is disclosed.